Linear constant current source composed of integrated operational amplifier

The linear constant current source circuit composed of an integrated operational amplifier is composed as shown in the figure. Two operational amplifiers (one piece of 324) constitute the comparison amplification link, and the BG1 and BG2 transistors constitute the adjustment link. RL is the load resistance, RS is the sampling resistor, and RW is The circuit provides the reference voltage. Working principle: If Uin decreases due to power supply fluctuations and the load current decreases, the sampling voltage US will inevitably decrease, so that the difference between the sampling voltage and the reference voltage (US-Uref) will inevitably decrease. Since UIA is an inverting amplifier, its output voltage Ub = (R5/R4) × Ua will inevitably increase, so that the US can be raised back to its original stable value through the adjustment process, ensuring the voltage stability of US and thus making the current stable. . When Uin rises, the principle is the same as before. The circuit uses the closed-loop feedback system to make US drop to the original stable value, thereby making the current constant. Adjust RW and change Uref to make the current value continuously adjustable between 0 and 4A.